Male factor infertility problems may be present in 50% of infertile couples. Most commonly, male infertility is attributed to idiopathic causes with limited therapeutic options available. To further define the pathophysiology of abnormal sperm function we must first expand our knowledge of normal sperm physiology in vivo. Specifically, mechanisms of sperm storage, survival and capacitation in the oviduct are poorly understood. This is due in part to the difficulty of mimicking the oviduct in vitro. Recently, the in vitro coculture (COC) of sperm and oviduct epithelial cells (OEC) has been reported using animal models. Sperm attach to OEC in vitro and subsequently maintain superior motility, viability and capacitation rates over that seen for sperm in routine culture media. The general hypothesis of this proposal is that human sperm can interact with OEC in vitro and undergo biochemical changes, similar to those which occur in the oviduct in vivo; and that differing ability of sperm to undergo these changes in vitro can be used to identify additional categories of male infertility. Aim #1 seeks to establish an efficient, reproducible COC system for human sperm. Sperm function in COC with human, primate or bovine OEC will be compared to determine if animal OEC can be used for the system. Further work will compare sperm function in a system using cell-free OEC conditioned media with sperm function seen in direct OEC and sperm COC. In Aim #2, COC is evaluated as a sperm function test for fertile and infertile men. Sperm changes occurring during COC are quantified to determine if sublethal sperm defects in some men may interfere with sperm attachment of OEC, and subsequent survival and capacitation in COC. The possible therapeutic uses of COC for enhancing sperm function in vitro are also studied. Sperm attachment to the OEC tends to involve live sperm with intact membranes, such that COC may be a method to sequester the most healthy sperm from an ejaculate. The fertilizing capacity of such sperm are likely enhanced after exposure to the OEC and their secretory products. Aim #3 investigates the degeneration of sperm DNA during COC. In the past it has not been possible to study nuclear degeneration of sperm during storage in the woman's oviduct, although such disruptions in DNA could lead to conception failure or early embryonic losses. The COC system offers a unique opportunity to keep sperm alive in vitro, similar to the length of time they physiologically survive in women, and to evaluate DNA degeneration (in situ) which may occur during this extended survival time. The knowledge gained from these aims may: identify additional types of male infertility; provide new therapeutic protocols for infertile men; and identify aspects of sperm DNA degeneration which could result in early embryonic losses.